Metagenomic Profiling of Antibiotic Resistance Genes in Swine Manure Residues After Sarcophaga peregrina Larval Bioconversion Under Polystyrene Particle Exposure

Insect-mediated bioconversion is a promising strategy for livestock manure recycling, but its effects on antibiotic resistance genes (ARGs) in residual substrates remain insufficiently understood, especially under polystyrene particle exposure. In this study, swine manure was treated with Sarcophaga peregrina larvae under four concentrations of 100-nm polystyrene particles (PS particles: 0, 0.001, 0.01 and 0.1 mg/kg), and ARG profiles in air-dried residual manure were characterized. Larval treatment reduced manure mass by approximately 40% within 4 days, and reduction rates did not differ significantly among PS particle concentrations. However, larval treatment increased RPKM-normalized total ARG abundance relative to the corresponding controls, whereas the residue mass-adjusted relative ARG index remained below 1.0 in all larval treatment groups after incorporating residue mass. ARG richness and Shannon diversity were not significantly reduced. ARO-level turnover analysis showed both newly detected and no longer detected ARG types after larval treatment. PCoA and PERMANOVA indicated treatment-associated differences in resistome structure, with PERMDISP suggesting that dispersion also contributed. At class and mechanism levels, multidrug resistance and antibiotic efflux were dominant. These results indicate that S. peregrina larvae efficiently reduce manure mass, but their effects on ARGs are better described as residual resistome restructuring rather than ARG removal.